There is a growing desire to use point to multi-point services in wireless communication systems. In point to multi-point (PtM) services, one service is sent from a single point, such as a base station, to multiple points, such as multiple wireless transmit/receive units (WTRUs). Examples of point to multi-point services are multimedia broadcasts and multicast services.
In traditional point to point (PtP) services, power control allows for efficient use of radio resources. Power control allows a particular wireless transmit/receive unit (WTRU) to receive the PtP service at a desired quality of service (QoS) and minimize interference to other WTRUs.
In PtP, such as for the third generation partnership project (3GPP), when the WTRU's dedicated downlink physical channel is power controlled, that WTRU typically determines a target signal to interference ratio (SIR) based on the received block error rate (BLER) of the dedicated physical channel. The WTRU estimates the received dedicated physical channel's SIR. One approach to determine the SIR is as the ratio of received signal code power (RSCP) over the interference signal code power (ISCP).
When the WTRU determines that the SIR target value is greater than the calculated estimate of the received SIR value, the WTRU signals via the transmit power control (TPC) commands to the base station to increase transmit power of the downlink dedicated channel. When the SIR target value is less then the received SIR calculated estimate, TPC commands are generated to decrease DL transmit power.
One channel currently proposed for potentially supporting PtM services is the forward access channel (FACH). The FACH is a channel broadcast throughout a cell and the FACH is maintained at a power level so that any user in the cell can receive the FACH. As a result, adaptive power control mechanisms are not used for the FACH. One problem with the lack of FACH power control is that a high data rate service sent over the FACH will generate considerable interference. The FACH transmission power level needs to be set at a power level so that a WTRU at the periphery of the cell can receive the high data rate service at an acceptable quality.
Accordingly, it is desirable to have adaptive power control for PtM services.